a. Field of the Invention
The present invention relates to an on-line inspection technique for electronic components such as semiconductor devices, and more particularly it pertains to a method of checking electrical characteristics during the fabricating process at the stage that lead wires are bonded to semiconductor devices in order to detect and remove bad components.
b. Description of the Prior Art
Semiconductor devices serving as electronic components which are typically diodes, transistors, SCRs (Silicon Controlled Rectifiers) and ICs are usually completed as electronic components through a series of steps such that a semiconductor chip, which has experienced the fabricating process of "diffusion" to impart a required function thereto, is fixedly mounted by, for example, soldering onto a base or support. The base is called a stem, printed plate or lead frame. Thereafter, connection is established, with a lead wire, between the ohmic contact metal electrode on the semiconductor chip and a predetermined terminal or terminals of equipment by using an apparatus called a wire bonder. Subsequently, the resulting semiconductor device is molded with a plastic material or encapsulated in a metal can. In order to complete the production of the electronic component, there are needed the steps of checking various electrical characteristics required of the component at the end of the above mentioned fabricating process and of sorting out only good components.
The causes for electronic components using semiconductor devices to be classified as rejectable articles may be roughly divided into the following two: the bad condition noted within the semiconductor chip per se, and the poor technique of fabrication in the stage of bonding a lead wire.
The poor electrical characteristics of a semiconductor chip, mentioned above, are often found through a checking made by the use of a testing apparatus, called a prober, of a semiconductor wafer prior to being separated into semiconductor chips by dicing, and bad portions; i.e., bad chips, which have been separated from the wafer are removed. However, there have been cases where the above mentioned check-out or inspecting process is omitted for the sake of simplifying the fabricating process, or from the viewpoints of price, productivity and so forth. In these cases good components are segregated only through a final inspecting process.
The other cause for the development of bad components during the fabrication stages immediately preceding the bonding of lead wires can arise during the dicing and bonding steps, even if the inspecting steps such as check-out and selection of electrical characteristics have already been carried out by probing during the wafer stage. Such defects attributable to the dicing process and the bonding process have been considered in the past to be detectable only during the final inspecting step.
The frequency of the occurrence of bad components during the dicing process or bonding process is not negligible. Those bad conditions of components which occur during the subsequent resin-molding process or metal-can encapsulating process, intended for the completion of components as electronic components, are found mostly during the life test of the components or after the components are placed on the commercial market as goods. These bad conditions are not of such nature that they can be found readily by a final inspection of the conventional type.
The conventional simple inspecting process for finding rejectable conditions which have occurred during the bonding step is an inspection process allowing the molding or encapsulation of not only good components but also rejectable components. It is an inspecting process which will give an adverse effect on price and productivity, as brought about by waste of materials.